What are Common Mainframe Interview Questions?

Donn Saylor

Mainframe interview questions give a potential employer an idea of an applicant's knowledge regarding the operation, programming, maintenance, and testing of a mainframe computer system. A mainframe is an oversized digital computer that can serve hundreds of users and tackle computations on a large scale. Because of its unique characteristics, mainframes require specialized personnel to oversee their proper operation. Commonly asked mainframe interview questions will ensure a prospective employee has a thorough understanding of both mainframe basics and, depending on the job, more advanced knowledge of the system. Jobs in this field include mainframe operators, mainframe systems analysts, mainframe software developers, mainframe testers, and quality assurance specialists.

Many facets of mainframe operation can be covered in an interview.
Many facets of mainframe operation can be covered in an interview.

When preparing for a job interview in the field of mainframe operation, an applicant should first consider all aspects of the position. An employer will want to see if the candidate possesses the necessary familiarity with the many complex facets of mainframe computers. The mainframe interview questions will likely include queries regarding languages like COBOL and JCL. The interviewer may also ask about and test an applicant's knowledge of the mainframe transaction server CICS, the IBM mainframe disk file storage access method, and the data server DB2. In addition to defining these terms, the candidate will commonly be asked to explain how they work and how they fit in to the overall operation of the mainframe.

Most job interviews include questions about work ethic and past employment, as well as about practical skills.
Most job interviews include questions about work ethic and past employment, as well as about practical skills.

Specific mainframe interview questions might include: "What are the divisions in the COBOL program?", "How do you properly sort files in the COBOL program?", "What is a DD statement in JCL?", and "What is a SOC4 error in JCL?". Further questions may inquire about the proper table set-up for a CICS, the different types of VSAM files, and identification of the aggregate functions of DB2. The applicant's interview answers to these questions allow a job seeker to expound on his or her comprehension of the system and present his or her skill set to the employer.

Another set of frequently asked mainframe interview questions will revolve around troubleshooting. The interviewee may be prompted to explain the remedies for such situations as an 805 error, how to effectively eliminate duplicate files, or how to properly fix errors in a mainframe's Security Operation Center (SOC). These types of IT job interview questions give a prospective employer an accurate picture of how well an applicant will be able to handle the many intricate problems that may arise from working with mainframe computers.

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Discussion Comments


I work with mainframes and have been asked every one of those questions and more. Know common return codes of VSAM files, even the good ones. If you are going for a programming position, know language specifics, especially how to write bits of code. If you say you are an expert in COBOL, expect to prove it. Know the difference between CICS programs and batch. If you haven't done CICS programming, don't lie. Questions are normally asked for specifications of how to code them. Also, if you done DB2 coding in COBOL, be ready to answer questions regarding how to interface with the DB.

Mainframe interviews can get very specific. If you don't know something, or haven't dealt with it before just say so. Then say something like you are a very fast learner and would be able to pick it up quickly. If you have the other skill levels, they will appreciate the honesty. The questions and test will truly tell them anyway if you do not know it.


@Charred - I suppose I am the exception to the rule, then.

It wasn’t a mainframe computer job; it was good old database programming with a well known programming language.

After the interviewer went through the basic questions about my skills and experience, he handed me a piece of paper. It was a quiz of sorts, although he tried to reassure me that it wasn’t a quiz.

It had about ten programming questions and I was supposed to write down the answers in code. I blanked out. I had never, in my life, written code on paper; I had used the development environment with its pop ups, wizards and various tools.

I think I failed that non quiz, and I didn’t get the job. So my word of advice is, either way you should be ready, whether it’s to answer problem solving questions or to actually write code on a piece of paper.


@MrMoody - Yes, I agree, although I too have to admit that I’ve never worked with mainframes – so I can’t speak with any authority on the subject.

Most of my work in the job market has been with servers and web based systems. The specifics of the language are usually covered in computer certification quizzes and courses, not in general job interviews. However, there may be exceptions to the rule.


I’ve never had a computer job interview that went into the level of detail the article talks about for mainframe computer job interviews.

That being said, I have never worked with mainframes. However, most employers from my experience want to know about how you used a particular technology to solve a problem. They will pick up on how well you know the language and the particulars of the system by the way that you respond to this question.

I’ve also found that employers have pretty good noses, too; they can sniff out an applicant who is just throwing buzz words around to impress the interviewer versus someone who understands the technology and knows how to use it.

The latter, as I said, will focus on problem solving in his interview answers, not just language specifications.

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